Compressor



April 19, 1960 DARRQW ETAL 2,933,237

COMPRESSOR Filed May 20, 1957 2 Sheets-Sheet 1 Inventors: KennethADdrroJ v, Robe i MJo/wnson,

27 29 Their" Atorne y.

lllllllll ls; 5

COMPRESSOR Filed May 20, 1957 2 Sheets-Sheet 2 W x -HLL1LLJ\!JL)2) 1:\\\Il111fi1 m \11 $2; M I

I Pg. /0. I F/g. 80 40 I Q l "so I as I i i l a 30 I k 40 I 0 NORMAL. 1g 20 war I t "3 I g 0 1 a i i i I I 0 2a 40 60 a0 ma /20 M0 /60 I80 g /5NORMAL V cue/c FEET PER MINUTE a mics/1770M q m POINT n I 0 e I z 0 40 80 lop/2 0 I40/60/J9 invent-OPS CUE/C FEET PER IIl/VUTE De RobertH.-Jo/vnsor7, by flu! 77we/r- Attorney,

Unite States Patent COMPRESSOR Kenneth A. Darrow, Sprakers, and RobertH. Johnson,

Schenectady, N.Y., assignors to General Electric Company, a corporationof New York Application May 20, 1957, Serial No. 660,243

4 Claims. (Cl. 230-114) This invention relates to compressors and moreparticularly to a method and apparatus for eliminating pulsation in suchcompressors, and is a continuation-in part of our copending application,Serial No. 459,041, filed September 29, 1954, assigned to the sameassignee as the present invention and now US. Patent No. 2,814,431.

Pulsation is a serious problem in centrifugal or axial flow compressorsbecause it greatly reduces compressor performance at low flow rates andlimits the minimum flow rate possible. Such pulsation occurs when theflow rate in the compressor has been reduced to some value below thedesigned operating point of the machine either by throttling the inletor outlet thereof. Flow in both the impeller and diffuser of thecompressor becomes completely separated along the full length of theflow passages to produce pulsation. In large compressors, the pulsatingvibrations may destroy the machine.

Accordingly, it is an object of our invention to provide a novelapparatus to eliminate compressor pulsation.

It is another object of the invention to provide an improved diffuserstructure which will eliminate pulsation in the compressor.

It is another object of the invention to provide an improved compressorwhich has a longer, useful operating range.

It is another object of the invention to provide an improved compressorin which higher efficiencies are maintained at the low flow range nearor below the normal pulsation point.

It is another object of the invention to provide an improved compressorin which power input is reduced at extremely high flows by throttling atthe diffuser outlet.

It is another object of the invention to provide an improved compressorin which a stable non-pulsating flow is maintained from normal flow tozero flow conditions.

It is a further object of the invention to provide a novel method ofeliminating pulsation in a compressor.

In carrying out our invention in one form, a ring or flow preventionmember is positioned adjacent the periphery of the diffuser of thecompressor to provide a correct diffuser outlet area for all compressorflows, and to block the flow separation area of the diffuser.

These and various other objects, features and advantages of theinvention will be better understood from the following description takenin connection with the accompanying drawings in which:

Fig. 1 is a sectional view of a centrifugal compressor which embodiesour invention;

Fig. 2 is a top plan view taken along lines 2-2 of Fig. 1;

Fig. 3 is a view taken along lines 33 of Fig. 2;

.Fig. 4 is a sectional view similar to Fig. 1 with the ring member in aclosed position;

Fig. 5 is a sectional view of a modified centrifugal compressor;

Fig. 6 is a sectional view of a modified centrifugal compressori Fig. 6Ais a modification of Fig. 6 wherein a continuous difiuser ring isemployed;

Fig. 7 is a sectional view of a centrifugal compressor in which thefluid has partially separated from the walls;

Fig. 8 is a sectional view similar to Fig. 7 in which the fluid hascompletely separated from the walls;

Fig. 9 is a sectional view similar to Fig. 8 in which a closure memberis provided to block the low kinetic energy path;

Fig. 10 is a graph of compressor pressure rise plotted against fluidflow at variable speed; and

Fig. 11 is a graph of compressor pressure rise plotted against fluidflow at constant speed.

In Fig. 1 of the drawing, a centrifugal compressor, shown generally at10, comprises a casing 11 to define a chamber 12 therein. Casing 11comprises a lower wall portion 13 with an outwardly extending flange 14at its upper end upon which an upper wall 15 is seated by means of anoutwardly extending flange 16 at its lower end. Upper wall 15 isremovably secured to lower wall 13 by any convenient means, such as, forexample, a hook 17 with a wing nut 18 thereon. Hook 17 is pivotallymounted on a pin 19 which extends from a bracket 20 on the outer surfaceof wall 13.

An air inlet or aperture 21 is centrally disposed in upper wall 15. Anelectric motor 22 is preferably secured at the marginal edge of opening21 and spaced therefrom by any suitable spacing elements 23. Motor 22has a shaft 24 to project downwardly into chamber 12 on which is mounteda suitable centrifugal blower impeller 25 with a plurality of curvedblades 26 thereon. Centrifugal action of impeller blades 26 drives airfrom inlet 21 downwardly and outwardly toward the inner wall of casing11. Impeller 25 has a back plate or wall 27 and a forward wall 28 whichextend laterally outwardly to form a diffuser 29 with a plurality ofvanes 30.

A ring member 31, which is coaxial to and of slightly larger diameterthan the outlet diameter of diffuser 29, is located adjacent theperiphery of the diffuser. Ring 31 is maintained in position by threecams 32 which are mounted on the upper surface of wall 28. If it isdesired, any number of cams could be employed. As it is best shown inFigs. 2 and 3, each of cams 32 is provided with an axial groove 33 inwhich a ball bearing 34 slides. Each ball bearing 34 is supported by ahemispherical oilite bearing 35 on the rear wall of ring 31. Ballbearings 34 move ring 31 both rotatably and in an axial direction toopen and close the diffuser outlet.

Movement of ring 31 is controlled by a force multiplying or transmittingmeans, such as a circular section of rack 36 on the rear wall thereofwhich meshes with a pinion 37 on the upper surface of wall 28. A shaft38 connects pinion 37 to a pinion 39 outside: of casing 11. Pinion 39meshes with a rack 40 which is operated by a differential pressurecontrol device 41. Control device 41 comprises a casing 42 which issecured. to the outer surface of upper wall 15 by any suitable means,such as a bolt 43. Casing 42 is provided with apertures 44 and 45 whichcommunicate with the atmosphere and chamber 12, respectively. A piston46 is positioned within casing 42 to control rack 40 through a shaft 47.A shaft 48, which is connected to the opposite side of piston 46, isprovided with a spring 49 to control the movement thereof.

In Fig. 4, centrifugal compressor 10 is: shown with ring 31 in apartially closed position across the diffuser outlet. Such a position isattained when compressor 10 approaches zero flow condition to provide asmall exit area which maintains high velocity flow from the diffuseroutlet.

In the operation of centrifugal compressor 10, centrif ugal action ofthe impeller blades 26 drives air from inlet 21 downwardly and outwardlytoward the inner wall of casing 11. Ring 31 remains in a position abovethe diffuser outlet until fluid begins to separate from the wall ofdiffuser 29. The increase in pressure in chamber 12 to move piston 46outwardly within its casing 42 is produced-by an increase in speed whichresults from unloading impeller 26 with a decreased flow. Progressiveseparation of flow from the walls of impeller 26 and diffuser 29 isproduced by this decreased flow which is' seen from continuityconsiderations. Piston shaft 47 moves rack 40 to mesh with pinion 3 andturn pinion 37. Pinion 37 meshes with rack 36 to cause ring 31 todescend over the diffuser outlet. Such closure of partial flow blockageprevents fluid in ditfuser 29 from separating completely from the wallthereof. As a decrease in pressure occurs in chamber 12 piston 46 movesoutwardly to slide ring 31 up from the diffuser outlet. The closure,which is provided by ring 31 eliminates pulsation which would otherwiseresult upon continuous separation of fluid from one wall of impeller 25and diffuser 25 In Fig. 5, a modified compressor is shown in which theoutlet ofdiifuser 29 is tapered to position a tapered ring 31 thereon.Ring 31 is supported within casing 11 by a control device 50. Device 54}comprises a base 51 which is secured to the inner wall of casing 11 byany suitable means, such as bolts 52. A member 53 is secured to base 51to support a cylinder 54 in which is positioned a piston 55 with aconnecting rod 56. A bracket 57 on the outer surface of ring 31 isconnected to a bracket 58 on the inner casing wall by a spring 59. Rod56 is secured to bracket 57 by nuts 6%). Spring 59 tends to retain ring31 across the diffuser outlet. Air flow through diffuser 29 forces ring31 upwardly from the outlet thereof. A decrease in fluid flow allowsring 31 to form a closure for diffuser 29 until normal flow is attained.Such closure prevents separation of the fluid flow from the walls of thediffuser to prevent pulsation.

In Fig. 6, a modified ring member 61 is shown which comprises lower andupper continuous body portions 62 and 63 with a plurality of spacedapertures 64 in a circumferential row in the intermediate portiontherebetween to provide air passages. Member 61 may be used incompressor 16 in Fig. l to limit the fluid flow and power input thereof.In the operation of compressor it? with member 61 at high fluid flow thelow pressure in chamber 12 positions body portion 62 across the diffuseroutlet. If flow is reduced to the design point, the increased speed ofthe motor and impeller raises the pressure to move apertures 64 inalignment with the diffuser outlet to give unrestricted flow. Furtherthrottling increases the speed and pressure of the compressor motor toposition upper body portion 63 of ring 61 across the diflus er outlet atvery low flow,

The modification as disclosed in Fig. 6 may be more clearly understoodwhen, for example, it is applied to the well known tank type vacuumcleaner wherein a motor driven compressor is connected by means of aflexible tube to a rug cleaning tool or nozzle. The vacuum or lowpressure conditions created at the nozzle through the action of thecompressor serves to remove loose particles or dirt from the rug orother surfaces. Assuming now, in the first instance, that the tool israised from the floor or, as is generally done, removed from the tubefor the purpose of changing to another tool. Under these condtions,there is a high flow rate of air through the compressor and a resultantlow pressure. This low pressure which also exists. in cylinder 12 isjust sufficient to overcome the biasing action of spring 49 to movepiston 46 and gears 4t), 3%, 37 and 36, to position the first or lowerportion62 of ring 61 .over the diffuser outlet, and effectively reducethe power input to the motor which may exceed safety requirements due toan unloaded compressor. In the second instance, assume that the tool isbeing applied to a surface for cleaning thereof. In this condition flowthrough the tool or nozzle is reduced and consequently flow through thecompressor is reduced to a predetermined design point. mits an increasein speed and efl'iciency of the impeller, with a resultant rise inpressure. This pressure within cylinder 42 acts against piston 46 toovercome the biasing force of spring 49 and accordingly position thering 61, through the aforementioned gears, so the second or intermediateportion with openings 64 are in alignment with the diffuser outlet andnormal flow conditions are established. In the third instance, assumethat the cleaning tool or nozzle is pressed against the surface or theopening becomes otherwise restricted by large particles taken up by thecleaning process. In this condition, the low flow rate permits an evenhigher r.p.m. of the compressor with a resultant increase in pressure tothe pulsation range. This increase in pressure serves to progressivelymove piston 46 in cylinder 42 to position the upper or third portion 63of ring 61 over the diffuser outlet. The problems or disadvantagesassociated with an uncontrolled compressor to this exemplary applicationis in the first instance, high flow conditions and thus a high powerinput to the motor drive, an input, in watts, which may exceed safetyrequirements of the electric motor and the conductor thereto, and in thethird instance deleterious pressure pulsations. I

While the preferred form of this invention has been specificallydescribed, other modifications may be equally applicable. In thisrespect, reference is now made to Fig. 6A. In Fig. 6A, there is shown aring 61', having no openings, which may also be employed in theinvention disclosed in Fig. 1 together with the control device 41. ofoperation is, first, a high flow rate accompanied by a low pressure;second, a reduced flow rate accompanied by a higher pressure; and,third, a still further reduced flow rate accompanied by a still higherpressure. Therefore, in each instance an increasing pressure must serveto successively position ring 61 first to partially close the diffuseroutlet, second to open the diffuser outlet and third to again partlyclose the diffuser outlet. In order to move a solid ring 61' to each ofthese three positions through the unidirectional movement of piston 46,some means would be necessary to reverse the direction thereof.Alternately, however, in one form of this invention, cam surface 33 ofFig. 3 may be in curved form 33, as shown in Fig. 6A, having ahorizontal section 65 between two slowly descending sections 66 and 67.In this manner, with respect to the first condition of the sequence ofhigh flow, low pressure, the ring 61 is positioned through the action ofball 34 in section 67 of cam groove 33 partially covering the diffuseroutlet. During the second condition of increasing pressure and reducedflow, movement of piston 46 serves to position ring 61 through theaction of ball 34 engaging section 65 of cam groove 33 to the optimumcleaning position of opening the diffuser outlet. Upon the thirdcondition of the sequence, of reduced flow and still higher pressure,continued movement of the piston 46 further rotates ring 61 where balls34 engage section 66 of cam groove 33' and ring '61, again partiallycovers the diffuser outlet. It should be noted that during nonoperationof the compressor, or conditions of very low pressures, spring 49positions ring 61' to the position wherein the balls 34 engage section67 of cam groove 33.

There has thus been described a compressor control which automaticallyprovides proper flow for all throttling conditions at a. compressorinlet.

In Fig. 7, fluid which is shown by arrows 65 is forced from the airinlet through impeller 25 and diffuser, toward the inner wall of thecompressor casing. Initial separation of fluid from the walls of theimpeller and diffuser is shown by areas 66 and 67. Fluidwhich hasReduced flow then per-' As heretofore described, the exemplary sequenceseparated from the impeller wall reverses its direction of flow as shownby arrow 63.

in Fig. 8, pulsation conditions are shown in a conventional compressorwhich is not provided with a member 31 to break a continuous low kineticenergy path which is designated 69. Path 69 is produced by completeseparation of fluid along the full length of the flow passage.Pulsation. is caused by a feedback through low kinetic energy path 69 ofair which is shown by arrows Tit.

In Fig. 9, ring member 31 prevents complete separation and pulsation incompressor 19 because a correct diffuser outlet area is maintained forany particular flow. Thus, there is no low kinetic energy path throughwhich an air feedback occurs.

In Fig. 10, a graph of compressor pressure rise in head inches of water(H O) is plotted against fluid flow in cubic feet per minute at variablespeed. The speed of the impeller increased as the load was decreasedwith decreasing flow. As the normal pulsation point was approached, thediifuser outlet area was decreased to break the continuous low kineticenergy path to prevent separation. This outlet area was progressivelydecreased with decreasing flow to the zero flow point. The primaryreason that the pressure increased with decreasing how is the increasedspeed of the impeller.

in Fig. 11, a graph of compressor pressure rise in head inches of water(B 0) is plotted against fluid flow in cubic feet per minute at aconstant impeller speed of 15,600 revolutions per minute. This graphdiscloses the increase in operating range below the normal pulsationpoint through the use of ring member 31. All of the pressure rise willoccur centrifugally in the impeller at zero flow.

As will be apparent to those skilled in the art, the objects of ourinvention are attained by the use of a ring member which is positionedadjacent the periphery of the diffuser of the compressor to provide acorrect diifuser outlet area for allcompressor flows. It will beappreciated by those skilled in the art that while specific cooperatingmechanical structures have been described, other apparatus can beemployed to operate the ring member in response to pressure variationswithin the compressor.

While other modifications of this invention and variations of apparatuswhich may be employed within the scope of this invention have not beendescribed the invention is intended to include all such as may beembraced within the following claims.

What We claim as new and desire to secure by Letters Patent of theUnited States is:

l. A compressor control which comprises in combination, a taperedimpeller, a diffuser surrounding said impeller, a casing surroundingsaid diffuser, a movable annular ring member surrounding said diffuseroutlet movable to cover and uncover said diffuser outlet, andunidirectional means operatively connected to said annular ring memberto position said annular member throughout a position range includingpartially covering the diffuser outlet, second, uncovering said difiuseroutlet, and lastly, partially covering said diffuser outlet, saidunidirectional means responsive solely to a pressure rise within saidcasing for positioning said annular member throughout said range in thesaid range in the given sequence, said movement of said annular ringmember being from the said tapered side of said impeller towards theother side.

2. A compressor control which comprises in combination, an impeller, adiffuser surrounding said impeller, a casing surrounding said diflfuser,an axially and rotatably movable anuular ring member surrounding saiddiffuser outlet and adapted to cover the difiuser outlet with theannular wall surface perpendicular to the flow from said diffuser, saidring member comprising a first annular continuous portion, a secondportion having a circumferential row of openings therein, and a thirdannular continuous portion, and means responsive to increasing pressurein said casing for unidirectionally positioning said ring memberthroughout a range of positions, said range including partially coveringthe diffuser outlet with the first continuous portion of said annularring, aligning the openings in said ring member with the diffuseroutlet, and thirdly, partially covering the diffuser outlet with saidthird continuous portion of said ring member.

3. A compressor control which comprises in combination, an impeller, adiffuser surrounding said impeller, a casing surrounding said diffuser,an annular continuous ring member surrounding said diffuser outlet andadapted to cover the diffuser outlet with the annular wall surfaceperpendicular to the flow from said diffuser, means for supporting saidannular ring for rotatable and axial motion, means responsive to thepressure in said casing for unidirectionally rotating said annular ringmember to move said annular ring member axially through a range of axialpositions, said range including a first position wherein said ringpartially covers the diffuser outlet, a second position wherein saidring uncovers said diffuser outlet, and a third position wherein saidannular ring partially covers said diffuser outlet.

4. In an electric motor-driven centrifugal compressor, means forcontrolling the pulsation of flow from the impeller and limiting thepower input to the motor drive which comprises, an annular ring memberinterjected into the flow of said impeller, axially and rotatablysupporting cam means for said ring, means responsive to a pressure risein said compressor to unidirectionally rotate said ring and at the sametime to position said ring axially during said pressure rise in asequence of operations including interjecting said ring into the flow ofthe impeller, withdrawing said ring from the flow, interjecting saidring into the flow.

References filed in the file of this patent UNITED STATES PATENTS1,813,747 Kirgan July 7, 1931 2,648,195 Wild et al. Aug. 11, 19532,671,635 Willi Mar. 9, 1954 FOREIGN PATENTS 133,892 Switzerland Sept.16, 1929 305,214 Belgium Ian. 29, 1928 986,680 France Apr. 4, 1951

